The invention relates to a rotary tablet press comprising a rotatingly drivable rotor, having a die plate comprising die holes and assigned to the die holes upper and lower punches, rotating synchronously with the die plate, whose axial movement is controlled by upper and lower control cams, having at least one filling station comprising at least one filling device for filling the die holes with material to be compressed, having at least one compression station disposed downstream of the filling station in the rotational direction of the rotor, comprising at least one compression device which presses the upper and/or lower punches into the die holes when passing through the compression station in order to press the filled material in the die holes, and having at least one ejector station, disposed downstream of the compression station in the rotational direction of the rotor, comprising an ejector device for ejecting the tablets press in the die holes.
The invention also relates to a method for pressing tablets in a rotary tablet press, comprising the steps: a rotor, having a die plate comprising die holes and assigned to the die holes upper and lower punches, rotating synchronously with the die plate, whose axial movement is controlled by control cams, is driven in a rotational manner, in the course of its rotation in at least one filling station, the die holes are filled with material to be compressed, in at least one compression station disposed downstream of the filling station in the rotational direction of the rotor, the upper and/or lower punches are pressed into the die holes, wherein the material filled into the die holes is compressed, the pressed tablets in the die holes are ejected in at least one ejector station disposed downstream of a compression station in the rotational direction of the rotor.
Such tablet presses typically comprise a machine frame in which the rotor is disposed in a rotational manner. The rotor is populated with a number of dies and an equal number of upper and lower punches. Typically, a die filling device, a dosing station, a pre-compression and main compression station, and an ejector station for ejecting pressed tablets, are located on an outer pitch circle. The pre-compression and main compression stations can each comprise, for example, an upper and lower compression roller. Here, the compression process of the powdered material, for instance, filled into the die holes begins already in the region in which the appropriate control cam guides the punch into the die hole. This compression process is then continued in the pre-compression station using a comparatively low pressing force. In the main compression station, the compression is then completed using a substantially greater pressing force than in the pre-compression station. The mechanical deformation behavior of pressed masses and granulates can vary widely and depends substantially on the respective powder mixtures of active agent, binding agent, disintigrant, filling agent, lubricant, etc. During tablet pressing in such tablet presses, a problem arises in the so-called covers in which cracks form within the pellets when the tablets are ejected out of the die holes. A further problem exists in that the tablets to be pressed do not always attain the required fracture resistance. Until now, it has been attempted to counteract this problem using a variation of the pre-compression force in the pre-compression station. In practice, however, the known procedure does not always lead to satisfactory results.
Starting from the described prior art as a background, the object of the present invention is therefore to provide a rotary tablet press and a method of the initially named type, with which tablets can be pressed that always have the required fracture resistance, wherein crack formation is reliably prevented.
For a rotary tablet press of the initially named type, the invention solves the object in that at least one oscillation generator is provided in the rotational direction of the upper and lower punches between the filling station and the ejector station that at least temporarily oscillates the upper and/or lower punches at least at the compression station and/or at the filling station and/or at least at an upper control cam and/or at least a lower control cam. For a method of the initially named type, the object of the invention is solved in that the upper and/or lower punches oscillate at least temporarily, between the filling station and the ejection station in the rotational direction, at least at the compression station and/or at the filling station and/or at least at an upper control cam and/or at least at a lower control cam.
The rotor is mounted, for example, in a machine frame and can be driven in a rotational manner about a vertical axis. The number of upper and lower punches corresponds to the number of die holes of the rotor. The upper and lower punches are usually guided in guides. They are controlled during circulation in a known manner using control cams. The material to be pressed can be a powder. Pharmaceutical tablets, for example, can be pressed. A dosing station is usually disposed downstream of the filling station. The filling station, the dosing station and the compression station are located at an outer pitch circle of the rotor aligned with the punches and die holes. Sometimes, only the upper punch is pressed downward into the die hole, whereas the lower punch is held in a fixed position in the die hole. It is also possible, however, that in the compression station the upper and lower punches are moved simultaneously or successively towards one another in the holes. In both cases, the material located on the lower punch in the die hole is compressed. Sleeves or dies can be disposed in the die holes that are then filled with the material to be pressed. In the ejector station, the upper punches are removed upward from the die holes in a known manner, and the lower punches are guided upward through the die holes, wherein they move the compressed tablets in the holes onto the surface of the die plate. From there, they are led, for example, by a deflector to, for example, an outlet which diverts them out of the press and leads them to further use, such as to packaging. Naturally, for instance, two filling stations and compression stations and possibly ejector stations can also be provided respectively at the press.
The compacting process of the, for example, powdered material filled into the die holes can be divided into several phases. In a first phase the particles are re-oriented. In a second phase the particles are elastically and plastically deformed. In the third and final pressing phase, the particles are bonded to each other. The invention is based on the recognition that inner tensions generated in the compressed tablets during these phases can lead to the initially mentioned crack formation and fracture resistance problems. Furthermore according to the invention, it was recognized that these inner tensions can arise during the compression procedure due to the inclusion of air. For avoiding this air inclusion, according to the invention the upper and/or lower punch compressing the material is vibrated during the compaction process of the, for instance, powdered material located in the die holes. For this purpose, one or more vibration generators are disposed in the area between the filling device and the ejector station. The punches can be activated by these generators, in particular, to vibrate in a vertical direction. However, additionally or alternately, vibrations in other directions are conceivable. The vibration of the punches can occur, in particular, during a main compression phase in the main compression station. However, they can also occur already during the pre-compression phase in a pre-compression station. According to the invention, it has been recognized in particular that it is advantageous already upon the upper punch entering into the die hole, before arriving at a pre-compression station, to vibrate the punch, controlled by an appropriate control cam (pull-down cam). The vibration leads to the fact that the material located in the die holes or the dies is distributed more homogenously, and in this manner the inclusion of air is reliably avoided. Thereby, in turn, cracks in the pellets are avoided during ejection from the dies. In particular, the powder particles to be pressed in the three compression phases described above are optimally distributed and bonded to each other. At the same time, the required fracture resistance of the tablets can be assured in this manner at all times.
The arrangement of the vibration generator(s) is possible at different locations substantially along the common vertical force progression axis. The vertical force progression axis extends in the vertical direction along the entire press, for example, through the centers of the possibly provided upper and lower pull-down cams or pre-compression rollers or main compression rollers. For example, a stimulation to vibration of the pull-down cams and the pre-compression rollers or main compression rollers, leads likewise to a vibration of the upper and lower punches controlled by these. A suitable control device can be provided. It controls the vibration generator(s) in the manner according to the invention.
Thus, according to the invention, air inclusions are substantially avoided. Thereby, inner tensions in the pellets are avoided, and the cover tendency is also reduced. This, in turn, minimizes tablet waste. At the same time, a higher fracture resistance and, in particular, the respectively required fracture resistance, is attained with a lower compression force. This in turn leads to an improved running smoothness of the press, and with it, to lower sound emissions. Also as a result, the wear, particularly of the press devices such as the compression rollers and the punch heads interacting with them, is reduced. The energy expenditure per tablet produced can be reduced, which also results in a cost reduction. According to the invention, the possibility of direct compression also exists. Thus, in the prior art, the powder to be compressed is frequently fed in advance to a granulating process in order to improve the subsequent suitability for tabletting the press masses in the press. According to the invention, this costly granulating process can be omitted.
According to one embodiment, at least one vibration generator can be disposed between the filling station and the compression station in the region of an upper and/or lower control cam for the upper and/or lower punch, thus in particular, at a pull-down cam, that at least temporarily vibrates the upper and/or lower punches while passing the upper and/or lower control cam. This embodiment takes into account the realization that it is advantageous for the punch to vibrate already upon entrance of the punch into the die hole.
According to a further embodiment, the compression station can comprise at least an upper and/or lower compression roller, which press the upper and/or lower punches into the die holes while passing through the compression station. In the pre-compression station, the material to be compressed is initially compressed using a comparatively low pressing force. In the main compression station, the compression is completed using a significantly higher pressing force than in the pre-compression station. In this case, the pre-compression station can correspondingly comprise an upper and lower pre-compression roller, and the main compression station can comprise an upper and lower main compression roller. However, instead of compression rollers, in principle, pressure rails or cam tracks, for example, can also be used. However, it is also conceivable to omit the pre-compression station.
According to a further embodiment, at least one vibration generator can be disposed at the compression station that at least temporarily vibrates the upper and/or lower punches in the compression station. If the compression station comprises a pre-compression station and a main compression station, at least one vibration generator can be disposed at the pre-compression station and/or the main compression station that at least temporarily vibrates the upper and/or lower punches in the pre-compression station and/or the main compression station. The vibration generator(s) can be disposed in particular along a vertical axis running through the centers of the upper and lower pre-compression rollers and/or main compression rollers, such that the punches vibrate while passing through the pre-compression and/or main compression rollers. In particular, the vertical force progression axis containing the vibration generator(s) can extend through the pre-compression station or main compression station.
The vibration actuators according to the invention can be of various types. For example, ultrasonic vibration generators and/or electrical vibration generators and/or mechanical vibration generators can be considered. Piezoelectric elements, for example, can be considered as electrical vibration actuators.
The vibrations of the upper and/or lower punches are superimposed on the progression of the pressing force during the compression of the material located in the dies, and have a higher frequency than the progression of the pressing force. Initially during the compression, the pressing force increases during the entry of the upper punch into the die, in particular, up to a maximum when the material is completely compressed by the punch. During subsequent removal of the upper punch from the die, the pressing force correspondingly decreases again. This pressing force progression repeats from punch pair to punch pair, and in total, has the progression of a standard sine curve. For attaining the advantages according to the invention, the vibration frequency forced upon the upper and lower punches should be substantially higher than the frequency of the pressing force progression. The appropriate vibration frequency depends, for example, on the properties of the material to be compressed, the compacting forces and the rotational speed of the rotor in the scope of the compression. Purely as an example, vibration frequencies are in the range of 50 Hz to 50 kHz.
According to a further embodiment, the upper and/or lower punches can be vibrated during the entire compression of material filled into the die holes. The vibration generators are then appropriately controlled in this manner by a control device. According to this embodiment, the entire compression procedure in the dies is advantageously influenced in the manner according to the invention. If a pre-compression station and a main compression station are provided, the punches can vibrate, for example during the entire compression in the pre-compression station and main compression station and already during the pass of a pull-down cam. However, it is also possible that the punches vibrate, for example, only during the compression in the main compression station.